The Trump campaign and the Republican National Committee are moving quickly and aggressively to head off the fledgling effort to stage a revolt at their convention next month in Cleveland, hoping to spare the party an embarrassing spectacle that could deeply wound the presumptive nominee.

They are employing hard-nosed tactics, warning delegates that attempting to undermine Donald J. Trump’s claim to the nomination violates party rules, and threatening to deny speaking slots to Republicans they deem disloyal for not backing him.

“If there’s no endorsement, then I would not invite them to speak,” Mr. Trump said in an interview, adding that former rivals like Senator Ted Cruz of Texas and Gov. John Kasich of Ohio should not expect to address the convention if they continue to withhold their support.

The R.N.C. and the Trump campaign are also installing loyal party stalwarts in key party positions to help ensure that they maintain control of the convention if rogue delegates attempt a disruption. And they are trying to discredit Republicans who are advocating an interpretation of party rules that would allow delegates to vote for anyone they want on the first ballot.

Their moves are intended to buttress Mr. Trump as he confronts a faction of Republicans who, emboldened by his recent missteps, say their efforts to stage a convention coup are gaining more support. In the last week, prominent Republicans like House Speaker Paul D. Ryan and Gov. Scott Walker of Wisconsin have breathed new life into these efforts by saying that delegates should be free to follow their consciences instead of being committed to back a candidate.